1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing equipment, more particularly the plasma reactor chambers for vacuum conditions for processing substrate material.
2. Discussion of the Background
The fabrication of integrated circuits in the semiconductor industry typically employs plasma to create and assist surface chemistry within a plasma reactor. Such plasma reactor is required to remove material from and deposit material to a semiconductor substrate. In general, plasma is formed with the plasma reactor under vacuum conditions in a vacuum chamber by heating electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Gas is introduced via a gas inject plate into the plasma processing chamber. The gas is subsequently heated by a strong electrical field between an upper electrode assembly and a substrate. Moreover, the heated electrons can have energy sufficient to sustain dissociative collisions. Therefore, a specific set of gases under predetermined conditions (such conditions are for example the chamber pressure, gas flow rate etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the chamber. Such processes can be for example the etching processes where materials are removed from the substrate or deposition processes where materials are added to the substrate.
The plasma can be formed by a capacitively coupled plasma (CCP) source, an inductively coupled plasma (ICP) source, an electrostatic radio frequency (ESRF) source, or any combination thereof, and with or without DC magnet system. Alternately, the plasma can be formed using electron cyclotron resonance (ECR), by launching a Helicon wave or by a propagating surface wave.
The semiconductor manufacturing industry is a very competitive marketplace. Constant efforts are done to reduce the cost associated with semiconductor processing by reducing the size of the apparatus, number of parts in the chamber, and the required maintenance of the chamber. Since a vacuum chamber is expensive and it is desirable that only a small area needs to be vacuumized, ideally only the area between the substrate and the upper electrode assembly, a different design of the processing chamber might be more suitable for such processes.
In plasma processing chambers used throughout the semiconductor industry, the chuck assembly for holding the substrate inside the plasma processing chamber in a firm and precise position can typically be moved in vertical direction by a linear displacement device in order to change the distance between the substrate and the upper electrode assembly. The variation of the distance of the substrate to the upper electrode assembly is desirable to have the possibility to vary the plasma properties of the heated electrons bombarding the substrate in etching and deposition processes. The electrical field between the substrate and the upper electrode assembly is varied with the distance. In other words, the closer the substrate is to the electrode, the higher the electron temperature is. Additionally, the gas flow dynamics can be varied by changing this distance. Basically, the gas flow in the plasma processing chamber is directed from the gas inject plate of the upper electrode assembly to the pumping port of the processing chamber. The stream lines of the gas might be varied, depending on the cross-section area between the side walls and the chuck assembly as well as the distance between the substrate and the upper electrode assembly. Thus, a movable chuck configuration can be used to vary process conditions in the chamber. However, these configurations have several drawbacks including the following.
First, movable chuck configurations can be more prone to particle contamination within the chamber. Specifically, since the linear displacement device should not be in a vacuumized area, the device is hermetically enclosed and protected by a bellows. The bellows surrounds the linear movement device and is fixed to a lower portion of the chuck assembly and the processing chamber base wall, enclosing the linear displacement device entirely.
While the substrate being processed has a controlled temperature, the lower portions of the processing chamber might have a lower temperature close to the room temperature, still allowing the chemicals to react and to deposit contaminants on the chamber walls, and on the bellows itself. While the bellows is typically shielded from the substrate processing environment, existing shields do not adequately prevent contaminants from depositing on the bellows. If contaminants are deposited onto the bellows, such particles might flake off as soon as the linear displacement device is moved. Such contaminants can exit the area inside the bellows shielding and may circulate with the gas flow inside the plasma processing chamber, seriously interfering with the deposition or etching process, and can damage the substrate. Furthermore, since the bellows is a moving part, accumulation of particles thereon would decrease the functionality of the bellows, which would have to been cleaned or replaced frequently.
Another drawback of the existing plasma processing chambers having a movable chuck is the grounding of the substrate. In order to create an electrical field between the substrate and the upper electrode assembly, a return path for RF current has to be provided. Current chucks usually have a ground path through a metal bellows. However, such a ground path is not optimal, since it may have excessive reactive impedance, and is inductively long. A ground path may also be provided through the bellows shielding. A result of this might be an unequal distribution of RF potential on the chuck and therefore an inconsistent plasma could result, which is very unfavorable for any etching or deposition process